Master-Slave Control Scheme in Electric Vehicle Smart Charging
Contents
1. 0 as the system approaches complete fairness The fairness index is defined in 2 to indicate the fairness of the system TE aal 2 Even though the round robin algorithm seems fair the fairness index 13 shows that it favors the first user that starts charging over the users that arrive later In the fair charging algorithm when the second user s charging session overlaps that of the first user s charging session the server predicts the second user s charge time and the first user s stay time in order to create a fair charging schedule The schedule will allot each of the two PEVs the charge time required so that they leave with same charge time ratio The schedule will switch charging enough to avoid the risk of a large charge imbalance but not so much as to take up too much time switching When a third or a fourth PEV arrives then new fair charge schedules are created that takes into account the new user If the time to switch charging between PEVs is close to zero then the optimization algorithm can be executed The fairness could be maximized by continuously switching charging power between PEVs However there is a noticeable time delay in switching charging sessions between PEVs due to data pull method Thus the period of time to switch charging from one PEV to the next can be as high as minutes given hardware and network constraints If the system switched continuously between users much charge time would be wasted in the2. 3 Metering System The metering system in both level 1 and level 2 charging stations consists of a gateway and four meters The meter inside the charging station returns its power infor mation including voltage current frequency power factor and energy consumption to the gateway upon receiving the command of power information retrieval through ZigBee communication The meters need to join the ZigBee mesh network created by the ZigBee coordinator embedded in the gateway The function of the metering system also requires the association of the meters ID and the physical outlet numbers The detailed schematics of a four outlet metering system are shown in Figure 3 4 The Scientific World Journal n Gateway PARE puenak 3G ANT2 WiFi Ll WiFi ANT3 ZigBee Jl ZigBee Plug female 8 L2 m ZigBee M1 J4 Meter amp Meter volt a Pl ug male CD seus oan _ lt ak ource voltage J3 Plug female Y ANT5 ZigBee M3 y i A J6 eter amp eter volt Plug male e u EV2 J5 Plug female j ANT6 ZigBee M5 M M l pa 7 eter amp eter volt Plug male e re EV3 J7 Plug female ANT7 ZigBee M7 aus J10 Meter amp Meter volt Plug male D gt ee EV4 J9 Plug female FIGURE 3 Schematics of metering system 3 Proposed Control Scheme and Results for Level 1 EVSE The processes involving the collaboration between the server and the charging stations such as the smart charging algo rithm 13 safety requirement 14 and the RFID authentic
3. 30 18 A for Chl initially When the adjacent channel Ch2 is plugged in the maximum duty cycle is divided by 2 and becomes 15 9 A When the PEV at Chl is fully charged or unplugged the duty cycle of Ch2 is set back to the maximum duty cycle Ch3 and Ch4 present the same result Simple commercial charging stations can also be mod ified as smart charging stations by connecting a metering system and local controllers In the ClipperCreek case The Scientific World Journal Check EV plug in status System status Pona pilot signal wait charge minutes System status ilot signal detect EV E a System status 6 V offset calibration run pilot flow System status Check existing charging set duty cycle outlets System status Yes monitor EV EV take energy System status Check EV plug in plug in status status every 3 Pull up EV detected Setup duty cycle for all outlets No Relay off User submit charge Generate pilot signal EV ready to accept energy Wait till existing Turn on EV finish eae changing load Restore duty cycle for all outlets FIGURE 6 State machine of simple Current Sharing Algorithm the charging station model CS 40 provides the terminals for three stage current control 30 A 6A and 0A 19 To control the connectivity of the terminals a ZigBee based local controller with relay module is design
4. H Bhade R Lowenthal and P Mandal Network controlled charging system for electric vehicles through use of a remote server US patent US8138715B2 2012 6 D Baxter C F Hagenmaier Jr M T Tormey and R Lowenthal Electrical circuit sharing for electric vehicle charging stations US patent US8013570B2 2011 7 S Mal A Chattopadhyay A Yang and R Gadh Electric vehi cle smart charging and vehicle to grid operation International Journal of Parallel Emergent and Distributed Systems vol 27 no 3 2012 8 Y He B Venkatesh and L Guan Optimal scheduling for charging and discharging of electric vehicles IEEE Transac tions on Smart Grid vol 3 no 3 pp 1095 1105 2012 9 A Shepelev C Chung C Chu and R Gadh Mesh network design for smart charging infrastructure and electric vehicle The Scientific World Journal remote monitoring in Proceedings of the International Confer ence on ICT Convergence pp 14 16 Jeju Republic of Korea October 2013 10 P Kulshrestha L Wang M Y Chow and S Lukic Intelligent energy management system simulator for PHEVs at municipal parking deck in a smart grid environment in Proceedings of the IEEE Power e amp Energy Society General Meeting PES 09 Calgary Canada July 2009 11 S Yang W Cheng Y Hsu C Gan and Y Lin Chargeschedul ing of electricvehicles in highways Mathematical and Com puter Modelling vol 57
5. and transmits SOC data via a ZigBee wireless link to a charging station and then onto the charging controller However without insider knowledge of the PEV manufacturers identifying data location on the CAN bus could present a challenge for obtaining the SOC data Several charging algorithms are presented in 10 12 however none of them mentioned a method to achieve variable current and multiplexing control let alone the collaboration between the control center and the charging stations In order to fully utilize the power resource on the local grid collaboration between the master controller server and the slave controllers charging stations in the PEV charging infrastructure is required to manage the charg ing sessions and or control the current to the PEVs This ability is not incorporated into the current WINSmartEV design In this paper a master slave control scheme for the electric vehicle smart charging infrastructure is pro posed to enhance the performance and features of this smart charging infrastructure These improvements include hardware upgrades that will enable better collaboration between EVSE and server enhanced smart charging algo rithms improved safety requirements and incorporating RFID authentication and authorization into the VMM sys tem This paper is structured in the following way First the current version of WINSmartEV is outlined in Section 2 Next the proposed upgrades to the smart charging control sc
6. interchanged between the gateway meters and the control unit are through ZigBee communica tion The function of the ZigBee coordinator on the gateway is to handle the messages between the gateway and the end devices or routers including the meters control units and vehicle monitoring identification modules VMMs 9 on the PEVs In order to dispatch the commands and parameters to the desired devices the ZigBee coordinator needs to recognize and register the unique MAC addresses of the end devices or routers Since a number of devices communicate using ZigBee mesh network capabilities only one gateway is required in a geographic locale The current system has two types of controllers one with and the other without ZigBee communication The controller without a ZigBee module talks to the gateway directly through USB port with RS232 communication On the other hand the controller set with ZigBee commu nication consists of ZigBee coordinator and ZigBee end device The gateway talks to the ZigBee coordinator to dispatch or receive response from the ZigBee end device Both types of controllers require a RS232 USB adapter cable in between the gateway and controllers In order to ensure proper functionality the RS232 USB adapter cable must be compatible with the gateway When the 3G dongle is used for communication both the 3G dongle and RS232 USB adapter cable must be assigned a USB port and only the assigned USB ports should be used 2
7. long the PEVs have been present As more sophisticated algorithms are developed the central controller has the flexibility and extensibility to be updated to include these new algorithms Because it incorporates J1772 standards with cables that can be plugged directly into the PEVs the level 2 charger is required to turn on and off the power to the PEVs by controlling relays and rate the power that each PEV pulls by controlling the duty cycle of the pilot signal The hardware and firmware of the level 2 smart charging station local controller is designed and implemented in 16 In order to accelerate the response of the smart charging stations by reducing the traffic between the smart PEV charger and the control center a power information collector PIC in 17 is designed to collect the power information locally and relay it to the control center periodically The response time can be further reduced by pushing the infor mation to the control center thus a fast response smart PEV charging infrastructure is achieved However because the control scheme is server based the server will need to wait for T ait due to the communication delay and the response time of the charging station and the PEV In order to accelerate the performance of the system a master slave control scheme is required as proposed in Section 3 2 2 Communication System In 16 there is a multiple protocol gateway inside the smart charging station to provide commu
8. no 11 12 pp 2873 2882 2013 12 W Su and M Chow Computational intelligence based energy management for a large scale PHEV PEV enabled municipal parking deck Applied Energy vol 96 pp 171 182 2012 13 C Chung J Chynoweth C Qiu C Chu and R Gadh Design of fair charging algorithm for smart electrical vehicle charging infrastructure in Proceedings of the International Conference on ICT Convergence pp 14 16 Jeju Republic of Korea October 2013 14 C Chung E Youn J Chynoweth C Qiu C Chu and R Gadh Safety design for smart electric vehicle charging with current and multiplexing control in Proceedings of the IEEE International Conference on Smart Grid Communications pp 21 24 Vancouver Canada October 2013 C Chung A Shepelev C Qiu C Chu and R Gadh Design of RFID mesh network for electric vehicle smart charging infras tructure in Proceedings of the IEEE International Conference on RFID Technologies and Applications Johor Bahru Malaysia September 2013 C Chung P Chu and R Gadh Design of smart charging infrastructure hardware and firmware design of the variable current multiplexing charging system in Proceedings of the 7th Global Conference on Power Control and Optimization PCO 13 pp 25 27 August 2013 17 C Chung J Chynoweth C Qiu C Chu and R Gadh Design of fast response smart electric vehicle charging infrastructure in Proceeding
9. time when one outlet is tripped the microprocessor is able to reset the GFCI independently after the user unplugs the PEV without affecting other PEV s charging session Because the GFCI board is sensitive false alarms are easily triggered due to the glitch at the rising edge in the output signal of GFCI board In order to avoid triggering false alarms the local controller deglitches the output from GFCI board and shuts off the contactor Figure 11 shows the new relay control method to avoid GFCI false alarms In the new design the GFCI board feeds its output to the local controller Instead of controlling one leg of the contactor directly by GFCI board the local controller controls both legs of the contactor for different conditions The implementation of Non ZigBee Level 2 J1772 local controller with GFCI function is shown in Figure 12 In order to have the fastest response time the interaction between the GFCI board and the microprocessor is handled by the interrupt routine in the firmware as shown in Figure 13 In the implementation of the GFCI function four inter rupt pins are used to monitor the outputs from the GFCI board with a rising edge trigger In order to avoid the false alarms caused by the glitch at the rising edge after one interrupt trigger the outputs of the GFCI board are monitored by the digital input pins with 500 us delay in the interrupt loop If the controller detects that the output pin is HIGH it terminates
10. to the database once new tag ID is detected Notice that the local controller inside the charging station serves the trigger signal of PEV plug in status Once the PEV plug in status is detected the local controller pushes the status to the database In the authorization process if the tag ID corresponds to an authorized user account in the database the command to enable charging is sent out to begin PEV charging In the collaboration between master and slave controllers in RFID mesh network feature several issues including handshake request interval PEV approaching and leaving determination and exception condition handling are dis cussed in the following About the handshake request interval the maximum time for a two hop response is 2 seconds in 9 which means TZigBee has maximum value of 2 seconds Considering TAN read S With maximum value of 0 1 second Twat will have to be greater than 2 1 seconds per equation 1 As a result 2 1 second minimum waiting interval must be incorporated on the local controller Therefore an interval much larger than 2 1 seconds needs to be incorporated for detecting an approaching PEV Taking 3G communication delay presented in 10 into account the maximum round trip time of 3G is around 5 seconds which means the server will need to wait 7 1 seconds to receive a response to a data request As for PEV approaching and leaving determination in most cases the accepted speed limit in parking lot i
11. DOE fund 20699 amp 20686 Smart Grid Regional Demonstration Project This material is based upon work supported by the United States Department of Energy under Award no DE OE000012 and the Los Angeles Department of Water and Power Neither the United States Government nor any agency thereof the Los Angeles Department of Water and Power nor any of their employees make any warranty express or implied or assume any legal liability or responsibility for the accuracy completeness or usefulness of any information apparatus product or process disclosed or represent that its use would not infringe privately owned rights References 1 R Gadh S Mal S Prabhu et al Smart electric vehicle ev charging and grid integration apparatus and methods US patent PCT international patent no US20130179061A1 WO2011156776A2 WO2011156776A3 PCT US2011 040077 US13 693 2010 2 R Gadh A Chattophadhyay C Y Chung et al Intelli gent electric vehicle charging system US patent PCT inter national patent no WO2013019989A2 WO2013019989A3 PCT US2012 049393 2011 3 R Gadh C Y Chung L Qi and C C Chu Network based management for multiplexed electric vehicle charging US patent PCT international patent no US20130154561A1 US13 691 709 2011 4 R Lowenthal D Baxter H Bhade and P Mandal Network controlled charging system for electric vehicles US patent US7956570B2 2011 5 D Baxter
12. Hindawi Publishing Corporation The Scientific World Journal Volume 2014 Article ID 462312 14 pages http dx doi org 10 1155 2014 462312 Research Article Hindawi Master Slave Control Scheme in Electric Vehicle Smart Charging Infrastructure Ching Yen Chung Joshua Chynoweth Chi Cheng Chu and Rajit Gadh Department of Mechanical and Aerospace Engineering University of California at Los Angeles 420 Westwood Plaza Los Angeles CA 90095 1594 USA Correspondence should be addressed to Ching Yen Chung chingyenchung ucla edu Received 28 February 2014 Accepted 18 March 2014 Published 26 May 2014 Academic Editors N Barsoum V N Dieu P Vasant and G W Weber Copyright 2014 Ching Yen Chung et al This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited WINSmartEV is a software based plug in electric vehicle PEV monitoring control and management system It not only incorporates intelligence at every level so that charge scheduling can avoid grid bottlenecks but it also multiplies the number of PEVs that can be plugged into a single circuit This paper proposes designs and executes many upgrades to WINSmartEV These upgrades include new hardware that makes the level 1 and level 2 chargers faster more robust and more scalable It includes algorithms that provid
13. a tion and authorization 15 are the prior arts in publications In order to fully utilize the power resource on local grid and improve the performance of the PEV charging infras tructure in the management of charging sessions or current control the collaboration between the master server and the slave local controller is required Therefore a master slave control scheme for the electric vehicle smart charging infrastructure is proposed to enhance the performance of the features including smart charging algorithms safety integration and RFID authentication and authorization The proposed control scheme involves a server based central controller and local controllers inside the charging stations The details of the collaboration scheme for the level 1 EVSE is presented in this section and the details for the level 2 EVSE will be presented in the next section RFID authentication and authorization will be discussed in Section 5 3 1 Local Controller Design In current level 1 charging station design 1 3 there is no local controller inside the charging station When the data pull method sends a power information request command from the server to a charging station the signal must pass through the internet and through a 3G network before it reaches the gateway of the charging station Then the gateway relays the power information request command to the specific meter it is meant for When the gateway receives a reply from the meter i
14. and parameters No Reset whole a system Change system Enable disable charging status 1n state machine Dut l pele Duty cycle change change Switch on off safety Manual switch relay Return Status request duty cycle and EV plug in status RS232 w interrupt end FIGURE 13 Local controller firmware flow chart the authentication process at a smart charging station allows charging authorization to take place at the moment of PEV arrival without user involvement The mesh network provides robust connections between PEVs and charging stations in a real world environment subject to signal blocking conditions The ZigBee routers in the VMMs serve as RFID tags while the ZigBee coordinator attached to the Gateway in the charging station serves as the RFID reader The unique 64 bit MAC address of each ZigBee device is utilized as an RFID tag The charging authentication process includes ZigBee MAC address retrieval user authorization and PEV plug in status detection When the charging station detects the PEV at a distance the received signal strength indication RSSI of the handshake serves as the metric for identifying a PEV approaching a charging station The PEV plug in status detection is used to identify the presence of a PEV at a charging station and to associate the vehicles ID with a particular channel The mesh network RFID is developed based on existing hardware without a
15. ation through a multiple protocol gateway The central server functions as the master controller while the local controllers embedded in the charg ing station serve as the slave controller in the infrastructure 4 1 Local Controller Design The current level 2 chargers have a ZigBee based local slave controller with multiple func tions including the pilot signal generator pilot signal monitor safety relay controller and autoreset function as implemented in 16 In this design three microprocessors are utilized to fulfill the functionality In the current practice because each charging station is equipped with a multiple protocol gateway the information exchange between the charging stations can be fulfilled by WiFi or Ethernet Therefore the ZigBee function on the local controller is indeed a redundant The Scientific World Journal FIGURE 5 Simplified J1772 EVSE controller without ZigBee function 1 RS232 module 2 Pilot signal generator monitor 3 Aduino Mega2560 communication channel In order to simplify the design and enhance the features and functionalities the ZigBee module has been removed and a more powerful microprocessor ATMega2560 with more input and output pins I Os has been added as shown in Figure 5 The pilot signals are created by ATMega2560 s internal timer and monitored by its analog input pins In this design only one microprocessor is used to fulfill the aforementioned functionality With
16. ave control scheme for the PEV smart charging infrastructure This scheme includes adding a power infor mation collector PIC to the level one EVSE that not only makes it faster and more scalable but also it enables the level 1 charger to execute operations within the EVSE itself With these features the level 1 EVSE can execute simple charging algorithms such as round robin locally Furthermore these enhanced capabilities allow the server to control the level 1 charger as a slave making the network structure more robust The hardware for level 2 EVSE has been updated in order to simplify the design and enhance its features and functionalities This update includes removing the redundant ZigBee communication system and updating the micropro cessor to a more powerful one These updates allow the implementation of a power sharing algorithm locally This is the simplest algorithm for level 2 charging Furthermore a fair charging algorithm appropriate for the level 2 EVSE is proposed This charging algorithm is calculated on the server side and executed with minimal instructions on the EVSE side Enhancements to the GFCI system have also been proposed that runs a system check to ensure that the GFCI system is operating properly and will shut off power when required in order to prevent hazards Algorithms have also been proposed to enhance the capa bility of the VMM system These enhancements will include the capability to automatically authenti
17. cate and authorize each PEV as it approaches the EVSE This allows the user to drive up to the EVSE and connect the cable These algorithms control the system to automatically do the rest so the user does not have to log into the server to begin charging Every PEV that is purchased instead of a dedicated fossil fuel burner is a good step in the direction of energy independence and lower greenhouse gas emissions As ever more of these PEVs hit the road sufficient charging infras tructure becomes even more important in proliferating PEVs throughout the car market With its new enhanced ability to multiply the number of PEVs serviced for a given electrical infrastructure WINSmartEV is poised to not only serve as a part of the nationwide smart grid system but as part of the larger push for PEV proliferation Disclosure Reference herein to any specific commercial product pro cess or service by trade name trademark manufacturer 14 or otherwise does not necessarily constitute or imply its endorsement recommendation or favoring by the United States Government or any agency thereof The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this paper Acknowledgments This work has been sponsored in part by a Grant from the LADWP
18. charging stations the charging algorithms at the local level could be more efficient than that at the server level By reducing the traffic between the server and the charging stations the improvements allow the control center to serve a larger system which enhances the capability of the existing WINSmartEV framework Nevertheless considering the calculation power of the microprocessor only certain simple charging algorithms such as round robin and Schedule Time can be imple mented in the microprocessor Thus with local charging algorithms implemented on the charging station level the server will only need to select the mode of the charging algorithms of each charging station This will save significant server computing resources With local charging algorithms implemented the control center could handle a larger smart charging system due to the reduction of traffic between the control center and the smart charging stations However because of the lack of computing power at the local level more complex charging and scheduling algo rithms still need to be implemented on the server No matter where the charging algorithm sits two major operation flows including ENABLE CHARGING and DISABLE CHARGING involve in the smart charging algorithms at server level In each operation flow two subprocesses including READ OUTLET ON OFF STATUS and READ POWER INFOR MATION need to be done This smart charging infrastructure can use its metering sys
19. command sets for the server and return values from the charging station are summarized in 16 Based on the experiments in 9 16 the server waiting time for the command sets in 15 16 is formulized and summarized in Table 1 In order to accelerate the servers performance the servers waiting time should be set to different values accord ing to the command set sent from Table 1 In the case of duty cycle change to shorten the servers waiting time Twaiting it can be set to be variable values based on Init and Igna rather than a fixed value to satisfy all conditions Moreover the simulation of pilot signal duty cycle change in 16 shows that it takes 30 ms to reach steady state This value needs to be compensated in the firmware of the local controller The authors in 18 concluded that charging algorithms with power information retrieval can be implemented locally in the charging station The system with embedded charging algorithms in which the traffic between the charging station and control center is reduced is faster than that with remote charging algorithms which are implemented on the server However from the experimental result the Fair Current Sharing Algorithm performs better than the Simple Current Sharing Algorithm with more users information Because the Fair Current Sharing Algorithm is based on the user s historical charging records it is more proper to implement it on the server With the charging stations equipped
20. dditional cost and pro vides traditional RFID benefits while adding mesh network capability In order to add authorization identification capability the firmware of the ZigBee coordinator inside the charging station and the software on the server need to be redesigned Rough processes in PEV charging authentication via RFID including ZigBee MAC address retrieval user authorization and PEV plug in status detection are presented in 15 However more details of the collaboration between the The Scientific World Journal master controller server and the local controller ZigBee coordinator need to be addressed for implementation The details of the proposed master slave control scheme for RFID authentication and authorization are presented in the following In 15 the authentication and authorization processes are periodically handled by the server In the authentication pro cess new PEV arrivals are checked by the ZigBee coordinator inside the charging station The server sends out the rgst command to check if new tag IDs have been registered after RFID reader initialization The stat command is later sent out to identify which charging station a newly arrived PEV is plugged into In real practice in order to accelerate the performance of the system the system needs to be modified to data push system Instead of periodically sending rgst command to retrieve the new tag IDs the ZigBee coordinator pushes tag IDs
21. e a more optimal charge scheduling for the level 2 EVSE and an enhanced vehicle monitoring identification module VMM system that can automatically identify PEVs and authorize charging 1 Introduction Every plug in electric vehicle PEV that is purchased instead of a dedicated fossil fuel burner is a good step in the direction of energy independence and lower greenhouse gas emissions As ever more of these PEVs hit the road sufficient charging infrastructure becomes ever more important in furthering the proliferation of PEVs in the car market In order to maximize the charging infrastructure that can be installed on a given electrical grid optimization needs to not only account for energy production but also account for constraints that may appear in the system at any level PEVs not only burden the energy production system but also pockets of PEVs in certain areas may strain the local grid and transformers Furthermore each new current electric vehicle supply equipment EVSE requires a dedicated electrical circuit that incurs expenses that limit the number of EVSEs that will be installed WINSmartEV 1 3 is a software based PEV monitoring control and management system that not only incorporates intelligence at every level so that charge scheduling can avoid grid bottlenecks but it also multiplies the number of PEVs that can be plugged into a single circuit This combination of optimizing the use of the electrical grid while multipl
22. e forth user s turn is treated as an overlap of the third users session Note that in practical implementation the maximum allowed current drawn is a discontinuous function of D based on J1772 standards 0 0 lt D lt 10 1 I 0 6 x D 1 10 lt D lt 85 7 I 2 5 x D 64 1 85 lt D lt 96 IL 0 D gt 96 The Scientific World Journal Submit charging session Overlap previous charging session Keep charging Multiplexing fair charging algorithm Duty cycle D1 lt 10 or D2 lt 10 Calculate duty cycle D1 for old user New user predictable Keep old charge time Use default prediction of Preda or meand stay time and calculate calculate duty cycle duty cycle D2 for new D2 for new user user Start current charging session FIGURE 9 Fair Current Sharing Algorithm Because 240 V with 30 A is the most common installation only the conditions in 8 are taken into account I 0 1 0 lt D lt 10 8 I 0 6xD 10 lt D lt 30 If the result of maximum current drawn I is less than 6 A the Fair Charging Algorithm with a 6 A maximum will be used instead of the Current Sharing Algorithm Similar to the Fair Charging Algorithm proposed in 13 the Fair Current Sharing Algorithm also counts on the accuracy of the prediction of user s stay time because the duty cycle calculation in 6 is based on the predicted stay time The
23. ed and implemented as shown in Figure 8 With ZigBee communication local charging stations can exchange information with each other in a local area With this design only one gateway is required per locale thus it saves in communication costs In order to implement a variable continuous current control on the simple commercial charging stations an extra circuit would need to be installed in between the charging station and the PEV to emulate the behavior of the PEV The design requirements for this circuit would include the ability to generate a pilot signal with variable duty cycle in response to the command from the server The design of the extra circuit which is beyond the scope of this paper is not addressed here UCLA PS8 level 2 box 002 09 27 2013 Current A Se LLL LCCC CeCe Lee q atictaatatatatatatetatetatctetatrtatcttatcts OHANMNAGTHRHOAMHtHTHOMTADHAMHTONA NNN NN N AN N N N N AN N N N N ANN GNAN Zan ee tee IN SOKSKSHSORRARNRKRRBGKKHKHKHBHKRAKRARH PS8L202LITA2 PS8L202LITA3 e PS8L202LITAO s PS8L202LITA1 FIGURE 7 Example of simple current sharing algorithm FIGURE 8 ZigBee based local controller for ClipperCreek charging station 4 2 Fair Current Sharing Algorithms To involve the smart charging algorithms at server level the server can select or disable local charging algorithms embedded in the firmware of the local controller No matter where the charging algorithm sits th
24. enhanced processing power simple charge schedul ing algorithms can be implemented on local device These simple current sharing algorithms can be designed and implemented by revising the firmware based state machine as shown in Figure 6 In the simple Current Sharing Algorithm the local controller assigns the available power to the desig nated outlet by setting up the duty cycle of the pilot signal before the Monitor EV stage The process of setting up the duty cycle is inserted in between the processes of Run Pilot Flow and Monitor EV The current sharing algorithm is based on the configuration of the box If there is no PEV charging in an adjacent channel the firmware will set the maximum available current to the given outlet Otherwise the firmware will divide the current for the PEVs to share Note that experimental results have shown a five second delay in the PEV response time 16 Once a PEV is unplugged the local controller restores the power to other PEVs In 16 the Monitor EV stage is handled periodically based on the timer interrupt flag In order to fulfill the J1772 standard to handle a faster PEV unplug detection the Monitor EV stage is moved to the main loop for continuously checking unplug status Figure 7 shows an example configuration of a simple Current Sharing Algorithm In this configuration Chl and Ch2 share one power circuit while Ch3 and Ch4 share another power circuit The firmware sets up the maximum duty cycle
25. f the system is fair every user s u p should be close to p u p Therefore both o u p and ulu p approach 0 if and only if the system approaches complete fairness for each user Here a new fairness index f is defined in B 1 A 5 The fairness index f approaches 1 if and only if both o u p and u u p approach 0 which is used to indicate the fairness of the system The parameter o o p is viewed as the convergence of the system o o p converges to 0 when the system is fair Figure 9 shows the flow of Fair Current Sharing Algo rithm When the second users charging session overlaps that of the first user the server still predicts the second user s charging time and the first user s stay time However instead of calculating charge time allocation for each PEV the server calculates the maximum current each PEV is allowed to draw current I based on the remaining energy consumption and the current share ratio p in 6 Instead of switching charging between the users charging sessions the server communicates the current I that each PEV is allowed by changing the duty cycles D of the pilot signal I D x 0 6 Piss x IMax x Tist E lza x t Dies E t Loi E PTarget x Imax I and I represent the maximum allowed current for the first and second user respectively Prarget is the target value of the current share ratio of the system The third user s session is treated as an overlap of the second user s session and th
26. he fair charging algorithm is implemented at server level In order to have better performance the calculations which rely on the historical data in the data base should still be finished at the server level The local controller inside the charging station is responsible to execute the charging schedule calculated by the server After the server calculates the charging schedule according to the selected charging algorithm it sends the charging schedule to the stations The charging stations control the charging sessions based on the schedule When some charging events happen during the charging sessions the local controller requests the server to update the charging schedule When the server receives the request of charging schedule change it calculates a new charging schedule for the charging stations 3 3 Safety Requirement Because the control of pilot signal for the level 1 charging station EVSmartPlug takes place within the PEV s trickle charge cable the automatic reset of GFCI is not required by UL certification Therefore a single commercial breaker with GFCI on the power source fulfills all the safety requirements 4 Proposed Control Scheme and Results for Level 2 EVSE The possible efficient control scheme of smart charging algorithms can be developed based on user preference and the local power capacity The central controller or server equipped with smart charging algorithms sends commands or schedule to the charging st
27. heme is discussed in 2 sections Section 3 for level 1 EVSEs and Section 4 for level 2 EVSEs Then an RFID authentication and authorization scheme is discussed in Section 5 2 Existing WINSmartEV Infrastructure There are three subsystems in UCLA WINSmartEV smart charging infrastructure including the control system the communication system and the metering system Some special features such as smart charging algorithms 13 safety requirement integration 14 and RFID mesh network system for user authentication and authorization 15 are developed based on the existing hardware and software Figure 1 shows the network architecture of WINSmartEV In order to implement the electrical power sharing concept a four outlet smart charging station connected to a single circuit is designed and implemented in 16 The one circuit to four outlet design is based on the limitation of normal circuit installation 30 A continuous and the mini mum PEV charging current 6 A defined in J1772 standard Theoretically the number of outlets could be 5 in order to fully utilize the maximum capacity of the circuit However in real practice it will easily trip the circuit breaker if any one of five PEVs draws a bit more than specified current Figure 2 shows the installation of a level 2 smart charging station and a level 1 smart charging station in a UCLA parking lot The details of the subsystems including control system communication system and meteri
28. ic field disturbance from the electromagnetic relay the GFCI board needs to be enclosed in a grounded metal surface box Once the safety feature is certified the UL does not allow firmware change by checking the CRC code of the firmware Since the safety function is not charging all the time in order to have the flexibility to add new features in the future the separation of safety feature from the other functions is needed Therefore one possible solution is to user extra microprocessor to handle the safety features while the original one deals with other features Thus the charging station can keep updating with new features while satisfying the UL certification 5 RFID Authentication and Authorization Scheme In current WINSmartEV system users are able to authen ticate themselves through a mobile app 1 3 A concept of mesh network radio frequency identification RFID charging authorization system in 15 which facilitates 12 Main loop I O and interrupt initialization Monitor EV charging RS232 w interrupt initialization Tie No flag Yes Timer interrupt plate machine initialization Pilot signal offset calibration Timer flag 0 Timer Timer flag interrupt 1 Timer interrupt end Interrupt by Wait 500 us GECI to avoid rising edge glitch Turn off relay Interrupt end and stop charging No The Scientific World Journal RS232 w interrupt Check comm
29. l anak Enable EV charging T waiting gt Tg F E E R TEVResp Turn on off relay manually rely T waiting gt Tg fact Disable EV charging d ang gt T3g ZigBee handshake response resp L waiting 0 ist Return all registered ZigBee MAC address T iing Tg T Toinne Ia Charging station status request Tiie P Tg jerge es ZigBee handshake request Titing 0 by sending out commands The charging stations can be reset manually or automatically on schedule as long as the connection between the server and the charging stations exists The pilot signal monitor can reset the whole system by turning off the switch on the power source of the charging station upon receiving the system reset command from the server After the charging station loses power the switch on the power source of the charging station is back to its normal position such that the charging station turns on again Any emergency action taken at the top level will have a delay time that depends on the condition of the wireless communication including 3G WiFi ZigBee and Cloud Thus a fast acting local unit is implemented to stop charging in case of an emergency In order to prevent electrical hazards there should be no voltage on the handle of the charging cable until it is plugged into a PEV The detection of the PEV plug in status is implemented in the state machine of the firmware of the control unit based on the J1772 standard The voltage of the pilot signal pin on the hand
30. l Journal of Gomputer Games Technology Advances in Software Engineering International Journal of Reconfigurable Computing Advances in Computational H man Conme ui Intelligence and Interaction Neuroscience Journal of Electrical and Computer Engineering Journal of Rob n
31. le should be 12 V when there is no PEV connected to the charging station After plugging in the PEV the voltage will be 9V or 6V depending on whether or not the PEV is ready to accept energy The PEV plug in status detection is implemented in the state machine in the firmware of the control unit Furthermore the charging station is required to shut off the power immediately to prevent the hazard of electric shock when there is an abnormal diversion of current from one of the hot wires The Scientific World Journal The ground fault circuit interrupter GFCI detects the differ ence of current between two hot wires and shuts off the safety relay when the difference has crossed the threshold amperage Unlike a traditional GFCI which requires manually pressing the reset button a pure hardware GFCI with a remote reset function is used to increase the reliability The power to the PEV can be controlled by the server the control unit of the charging station and the GFCI circuit In 14 one leg of the contactor is controlled by the pilot signal monitor while the other leg is controlled by the GFCI The pilot signal monitor can reset the GFCI by toggling the switch on the power source of the GFCI However in real world applications in order to have independent control over each GFCI channel instead of controlling the power source of the GFCI board the microprocessor generates the reset signal for the SR latch as shown in Figure 10 Every
32. ng system are described in the subsections The Scientific World Journal 2 1 Control System In this section the functionality of mas ter controller central server the slave controller charging stations is described in the following There are two types of charging stations level 1 charging stations that connect to standard 120 V household circuits and level 2 charging stations that connect to 208 V or 240 V circuits for faster charging The level 1 charger controls four EVSmartPlug outlets to provide power to the PEVs Because the PEV user plugs the PEV s trickle charging cable into the outlet to charge PEV the control system switches the outlet on and off in order to control the 120 V power to the trickle charging cable The level 1 charging stations are currently controlled by a server based central controller equipped with smart schedul ing algorithms Different algorithms including real time algorithms and scheduling algorithms can be implemented to control charging Round robin and FCFS first come first served are examples of real time algorithms Scheduling algorithms can be developed to include many factors such as time energy price energy amount or SOC For example a round robin algorithm which only turns on 1 channel and charges 1 PEV at a time is currently used to schedule charging in the level 1 EVSmartPlug station to share a single 120 V power source with four PEVs This algorithm only takes into account how
33. nication services for multiple functions To connect to the internet there are three types of methods including 3G Ethernet and WiFi 3G communication is required due to its flexibility and accessibility to be everywhere as long as the cellular signal exists especially where wired or WiFi communication is unavailable When using Ethernet for communication the gateway can directly connect to the internet with a static IP or a dynamic IP assigned from The Scientific World Journal Ethernet or WiFi Device Bo E t al Bi Station Station Station 1 lm 2 EV database Web server Database server Data collector RFID badge reader BA BE BE Station Station Station 2m nl nm UCLA EV network architecture FIGURE 1 Network architecture of WINSmartEV FIGURE 2 Installation of smart charging stations a DHCP router When Ethernet connection and 3G service are unavailable in a parking area WIFI or PLC can be used to connect to another gateway or router that does have an internet connection The EVSE s gateway can use a PLC module on its Ethernet port to connect to other gateways or routers connected to any electrical circuit on the same transformer When using WiFi for local communication the gateway needs to be setup as a client to connect to other gateways or routers In this case a port forwarding method is used on the other gateway or router so that the server can access the client gateway The information
34. ree major operation flows at server level need to be engaged including ENABLE CHARGING DIS ABLE CHARGING and PILOT SIGNAL DUTY CYCLE CHANGE In each operational flow there are three subpro cesses including READ METER ON OFF STATUS READ METER S POWER INFORMATION and READ OUTLET S STATUS The power information includes the voltage cur rent and active power The outlets status includes pilot signal s duty cycle safety relay on off status PEV plug in status and firmware based state machines stage To deal with a variable current charging station a fair current sharing algorithm is proposed Considering a variable current control charging station the fairness index is now related to the energy consumption E during the stay time T stays Which equals the average power P for the user in OBO P V DIE X z 3 T stay Stay The Scientific World Journal For a completely fair system the average power P of each user should be the same which means each user s charge rate is the same during the stay time For a fair enough system each users charge rate should be close enough Assuming V t is a constant a current share ratio p can be defined in I t xt bl Imax X Tstay p 4 where Imax is the current capacity The time sharing type of fair charging algorithm required for switching chargers can now be viewed as a special case of a current sharing algorithm with a discrete current instead of a variable current I
35. s 5 mph which means a PEV approaches a charging station by 4 5 meters every 2 seconds Assuming that the PEV parks 5 meters away from the charging station after a PEV is detected at a distance of 50 meters the station will have a maximum of 10 handshakes to determine whether the PEV is approaching or leaving Considering the exception condition handling when more than two PEVs come to the same charging station around the same time the charging station might not have a way to associate the IDs with the corresponding outlets In this case the server needs an exception handling process to handle the charging sessions If the arriving PEVs have different size of on board chargers the charging station is able to associate the IDs with outlets due to different current when charging However if the on board chargers are the same 13 size the server cannot associate IDs with the outlets In this case the server can later associate the charging sessions with IDs and outlets when the PEVs leave by detecting the PEVs RSSI the server can also associate the IDs and outlets by SOC when PEVs are fully charged before they leave If the PEVs with same size on board chargers arrive and leave around the same time without being fully charged there is no need to distinguish the charging session because their drivers will be billed for the same energy consumption 6 Conclusion In this paper we have proposed designed and implemented a master sl
36. s of the IEEE Green Energy and Systems Conference IGESC 13 Long Beach Calif USA November 2013 18 M Majidpour C Qiu C Chung P Chu R Gadh and H R Pota Fast demand forecast of electric vehicle charging stations for cell phone application in Proceedings of the IEEE Power amp Energy Society General Meeting National Harbor Md USA July 2014 19 Users Manual Model CS 40 Clipper Creek Auburn Calif USA 2014 http www clippercreek com pdf CS 40 20User 20Manual 20DLP 201P 20081205 20v03 pdf 20 H Bhade M Tormey D Baxter R Lowenthal and P Mandal Overcurrent and ground fault protection in a networked charging station for electric vehicles US patent US8072184B2 2011 m vI n ON Journal of Advances in Industrial Engineering Multimedia N Applied omputational Intelligence and Soft Computing e O International Journal of The Scientific P World Journal Sensor Networks Hindawi Publishing Corporation http www indawi com Volume 2014 i vwwhi Advances in Fuzzy Systems Modelling amp Simulation Hindawi Submit your manuscripts at http www hindawi com Journal of Computer Networks and Communications Advances in Artificial Intelligence International Journal of Advances in Biomedical magina Artificial d gt Neural Systems _ Internationa
37. switching process causing all users to be worse off Fairness maximization can be obtained while only switching charging once if exact stay time of the PEV is known If PEV s stay time is unknown fewer switching may often leave the charge time for each PEV lopsided and unfair Therefore the optimization of the fairness algorithm needs to take into account both the confidence of stay time and the time wasted in switching Therefore the Fair Charging Algorithm counts heavily on the accuracy of the prediction of user s stay time A forecast of users to the PEV charging station in 18 can be used for more accuracy on user s stay time If the prediction of the user s stay time is accurate fairness maximization can be obtained while only switching charging once There is no way for the charging infrastructure to retrieve a PEV s SOC status for the purpose of user s stay hour prediction unless extra devices VMM 9 for SOC data retrieval are equipped on the PEV The PEV s SOC status should not be considered available by using the current PEV charging station standard J1772 Therefore based on a users historical charging records for predictable people either u Tstay or a linear regression function is used to predict Tstay of the user For unpredictable people the average stay time of all users u u T is used for prediction A number of switches may be required if the prediction of the stay time is not accurate enough Currently t
38. t relays the response back to the server where the information travels back in reverse order With multiple meters requiring multiple requests each the aggregated round trip times cause slow performance In order to enhance the system s performance and shorten the response time of the system a device named the power information collector PIC 17 collects the power information locally in order to send it in to the server together as one packet By decreasing the number of communications required for status reports and control operations the PIC significantly decreases the delay time for switching PEV charging sessions or changing current to the PEVs In order to accelerate the response time of the charging station based on the design of the PIC a local controller The Scientific World Journal Figure 4 Local controller with controllability over power to outlets with the controllability over the power on the outlets is implemented as shown in Figure 4 Because the local controller is responsible for turning on off the outlet it reduces the round trips of command and response between the server and the charging stations Thus it accelerates the response time of the charging station Since the power information is available on the local charging station local charging algorithms can be realized on this design Certain charging algorithms can be implemented at the local level With less communication traffic between the server and the
39. tem to monitor the simple commercial charging stations such as Leviton ClipperCreek and Schneider so that the server can have control over these charging stations These charging stations can run switching type charging algorithms at the server level including a round robin algorithm or a fair charging algorithm 13 In order to have fair usage of power resource for every PEV user currently a round robin algo rithm is used to schedule charging in the multiplex charging system WINSmartEV In current practice the round robin algorithm is developed at the server level for the lack of local controller 3 2 Fair Charging Algorithm In order to appeal to more users a fair charging algorithm 12 is proposed to maximize fairness in the allocation of charge time for the smart plug charger The fair charging algorithm is designed for a switching type of charging stations such as the EVSmartPlug where only one PEV can charge at a time In this case each user s charge ratio T is defined as the ratio of the charging time T charge and the stay time Tsy in Tiare T 1 T stay The fairness of the charging system depends on how close all the users charge ratios t are to each other The fairness system can also be stated as follows for a given charging event every users mean charge ratio u t should be close to the mean charge ratio of every other user charging at the time ulu t Therefore both o u r and u o t must approach
40. the power to the PEV by turning off the specific relays thereby shutting off the contactor The GFCI of the outlet will be reset after the user unplugs the PEV When the GFCI of the outlet is triggered the system status of the state machine for the outlet will go to UNPLUG CHECK in which the local controller keeps monitoring the unplug status until the user unplugs the PEV The design of GFCI in 14 is triggered by 14mA differ ence between two hot wires on the positive cycle Since the design of GFCI only works for positive cycle of the AC if an abnormal diversion of current from a hot wire happens on the negative cycle the GFCI trigger will be delayed by 8 3 ms which is half cycle of 60 Hz In addition the GFCI circuit itself has approximately 1 ms delay In our proposed GFCI design compared to the maximum delay time of 8 3ms after the GFCI triggers which is half cycle of 60 Hz a 500 us delay time is acceptable To satisfy the safety requirement by UL Underwriters Laboratories certification the total The Scientific World Journal CT la 20k j O lu CT1b 1k 10k Reset ll Le Channel 1 out TLC2274 are D gt _ R i CD4043 lt FIGURE 10 Schematic of GFCI GFCI trigger reset External 220 V source Local System controller reset SW3 i 220 V source GFCI GFCI trigger reset Relay on off GFCI circuit Sw4 FIGURE 11 Schematic of safety control for the relay dela
41. with PICs set on data pushing mode the Fair Current Sharing Algorithm becomes more practical due to the improved response time of the system caused by the PIC Nevertheless it is also possible to obtain the user s stay time if the user s PEV is equipped with the VMM proposed in 9 which facilitates using the battery s state of charging SOC to predict the user s stay time In this way it is possible to implement the Fair Current Sharing Algorithm in the charging station 4 3 Safety Requirement As for the safety requirement for the level 2 charging station since the charging station controls PEV charging by the pilot signal the charging station is required to handle the GFCI function in both J1772 and UL standard Although the authors in 20 claim the GFCI of a networked charging station can be reset remotely no details of control methods or schematics are presented To provide a safe smart technology for charging PEVs a design for the safety system is presented in 14 which is implemented on all levels of control The administrator can turn the relays of the charging stations on or off and check their status 10 TABLE 1 Waiting time of command sets Comd Description and waiting time P Auto reset the charging station T waiting gt 0 5 Tg Taraso duty Change the duty cycle of pilot signal 1000 400 x Isna O 5XT3 Tiny 0 10 05 xT Tena 0 T waiting gt 310 0 5 x Tc Linit lt Te nal 5060 a 0 5 xX Les dca gt Te na
42. y of GFCI function should meet the requirement of the maximum value which is 24 9ms as per UL standard Overall the maximum delay in our proposed GFCI is 9 8 ms which satisfies the safety requirement by UL standard Besides the time delay requirement for GFCI the UL requires extra circuits such as GFCI tester and voltage monitor on the contactors to fulfill the safety requirement The GFCI tester is the circuit to test the GFCI function before energizing the contactor A solution for the GFCI tester is to add an extra wire in the current sensor from 12V dc source Then the local controller turns on a specified small current on this wire by using a digital output with a FET transistor and a power resistor The voltage detector will check the circuit to see if the contactor is welded before enabling the contactor If the contactor is welded which means the charging station cannot stop power to the outlet the system should stop providing service A possible solution is to use a voltage divider with power resistors to obtain small AC voltage Then a transformer is inserted in between to isolate the AC and DC voltage Later the local controller detects this FIGURE 12 Local controller for level 2 charging station with GFCI DC voltage with a Schmitt trigger through its digital input pin to see if there is voltage on the outlet of the charging station As mentioned before because the GFCI board is sensitive in order to reduce the magnet
43. ying the number of PEVs per circuit is a one two punch against the limits of the electrical infrastruc ture in charging PEVs Simple commercial charging stations such as Leviton and ClipperCreek which simply provide basic charging function without network features do not provide network services for smart charging purposes One exception is Coulomb Inc Coulomb devised its own proprietary network controlled charging system through a remote server 4 5 but these stations are not suitable for current sharing purposes because they only have one or two outlets A method of electrical circuit sharing for charging stations is proposed by Coulomb 6 however no details of charging algorithms are provided Since WINSmartEV is software based intelligent charg ing algorithms can be implemented and updated when needed The algorithms can be developed based on user s time energy price or energy amount A charging algorithm that relies on a smart phone interface for entering PEV data such as arrival and departure times and initial and final state of charge SOC is proposed in 7 The scheduling algorithm proposed in 8 requires the initial energy states of a PEV as the input These approaches are not valid unless the user provides the actual SOC data To solve this problem the authors of 9 propose a custom built module named vehicle monitoring identification module VMM which reads the in vehicle controller area network CAN data bus
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